This invention relates to an articulated arm for excavators or similar earth moving machines, to be used in particular for excavations lateral to the vehicle and parallel to its travelling direction.
Excavators are known to comprise an articulated excavating arm usually on the centre line of a rotatable turret on which a control cab is positioned, this arm being controlled hydraulically and provided with a scoop shovel or other similar excavating means (buckets, reverse buckets etc.). It is also known that in order to economically carry out excavating works extending in a mainly longitudinal direction, such as ditches or trenches, a machine of the aforesaid type must operate by moving parallel to the excavation direction, i.e. must be able to make excavations parallel to its travelling direction.
This is attained by positioning the turret in such a manner that when in its operating position, the excavating arm is positioned along the longitudinal axis of the vehicle, the machine then being moved along the path of the excavation which is to be made. Thus, the excavator operates by straddling the excavation which is being made, its wheels or tracks being respectively on each of the two edges of the excavation, the axis of which thus approximately coincides with the longitudinal axis of the vehicle.
This method of working is the only one possible in the case of normal excavators, because the articulated arm carrying the excavating shovel is able to make movements only in the plane in which it lies, so that it must be moved into a position coinciding with the excavation position, while at the same time maintaining said plane parallel to the direction of travel. These considerations are also valid for those machines which are not excavators which either are provided or can be provided with excavating arms, generally of small size, such as tractors or rough terrain vehicles (tractors provided at the front with a collection shovel and at the rear with an excavating bucket).
However, in practice it is often not possible to operate by straddling an excavation due to lack of space or because natural or artificial obstacles exist on one or both sides thereof, such as a wall, columns or trees.
In order to be able to operate rapidly and economically in such a case, it is then necessary to make the excavation laterally to the vehicle so that it can move to the side of the obstacles without colliding with them.
Certain devices have therefore been constructed in order to produce a lateral excavation parallel to the directon of travel. One of these, designed specially for application to excavators, consists of an articulated arm which is able to move outside the plane in which it lies, and is composed of a number of rigid arms hinged together.
A first arm, hinged to the rotating turret in such a manner as to be able to move in a plane perpendicular to the plane of rotation of the turret, carries a second short arm hinged to it in the same manner and terminating in a platform. A third arm is hinged to the platform by a pin perpendicular to the plane of rotation of the turret, and is thus able to move outside the plane in which the first two arms lie, in a plane parallel to the turret plane. A fourth arm is hinged to the third arm, and carries the excavating shovel, which is able to move in the plane in which the third arm lies. In this manner, by simultaneously rotating the turret and third arm, the plane in which the shovel lies (namely the plane of the third arm) is made to coincide with the excavation plane, while keeping the vehicle parallel to the direction of the excavation but displaced laterally to it, even though the turret is rotated.
However, all these devices have serious drawbacks, and in particular have the grave defect of making a very poor lateral excavation, with its walls uneven and not perpendicular to the working floor, i.e. that on which the machine moves, thus requiring costly manual finishing work. This is because the excavating shovel moves along a curved trajectory instead of perpendicular to the working floor, because the movement of the first arm of the vehicle takes place in a plane which is not parallel to that in which the shovel operates.